Tenths to charles e



S. G. DREW. TELEPHONE ,TRANSMITTER.

No. 511,882. Patented Jan. 2, 1894.

UNITED STATES.

PATENT @EETCE.

STEPHEN C. DREW, OF BOSTON, MASSACHUSETTS, ASSIGNOR OF THREE- TENTHS TOCHARLES E. JACKSON, OF SAME PLACE.

TELEPHONE-TRANSMITTER.

SPECIFICATION forming part of Letters Patent No. 511,882, dated January2, 1894.

Application filed January 23, 1898. Serial No. 459,317. (No model.)

To all whom it may concern:

Be it known that I, STEPHEN C. DREW, of Boston, county of Suffolk, Stateof Massachusetts, have invented an Improvement inTelephone-Transmitters, of which the following description, inconnection with the accompanying drawings, is aspecification, likeletters and figures on the drawings representing like parts.

In the telephone transmitters now in general use the diaphragm whichreceives the sound waves from the-voice, acts mechanically, eitherdirectly or through an interposed piece, upon one or more carbons, orother resistant buttons or electrodes included in the primary circuit ofan induction coil, the secondary circuit of the induction coilconstituting the line circuit extending to and including the distantreceiver. The sound waves produced by talking cause the diaphragm tovibrate, the vibrations of the diaphragm, both as to number andamplitude being mechanically transmitted to the resistant electrodes tomore or less vary the pressure upon or between the same, and thus causethem to interpose a greater or less resistance in the primary circuit ofthe induction coil to form an undulatory current therein correspondingto the undulations or variations in the sound waves. The undulations ofthe current in the primary circuit are reproduced by induction in thesecondary circuit of the coil and in the receiver included in thesecondary circuit, being made audible by the receiver. In transmittersof this class, the diaphragm is not free to vibrate to its fullestextent, the amplitude of its vibrations being limited, more or less, bythe action of the resist-ant electrode or electrodes pressing constantlyagainst it. To lessen this effect as much as possible it is necessary tomount the electrode or electrodes upon flexible or light springs, but bythus mounting the electrodes they are free to set up a counter vibrationof their own independent of the diaphragm,whichinjuriously affects thetransmission of sounds. The amplitude of the vibrations of a diaphragmis substantially the same at each side of its central position of rest,yet in transmitters of the class described wherein the electrodes pressdirectly or indirectly against the diaphragm at one side, the onlyvibrations which act upon and affect the electrodes are those atthe sideof the central position next to the electrodes, while the vibrations atthe opposite side of the central position do not affect the electrode toany extent. One-half the full vibratory movement of the diaphragm isthen practically unutilized in transmitting sound.

In my eiforts to improve the transmission of speech by means of thetelephone, I have conducted experiments to discover, if possible, somemeans whereby the vibrations of the diaphragm might be transmitted tothe resistant electrode or electrodes to vary the resistance offered bythe latter to the passage of an electric current, andyet leave thediaphragm perfectly free to vibrate under the undulations of the soundwaves, unobstructed and unhampered by any mechanical connections withelectrodes or other devices. It is a known property of a magnet that anyvariation in the strength of its magnetism causes the magnet to lengthenor shorten, or otherwise change its form, for example,if the magnetismof a bar magnet be strengthened its length will be found to haveincreased somewhat, and vice versa, if the magnetism be lessened it willbe found to have shortened. It is also a well known fact that when apiece of metal is moved toward and from a magnet it causes the magnetismof the magnet to be made either stronger or weaker, according as thepiece of metal is moved toward or from the magnet; In the course of myexperiments I have discovered that I may avail myself of this peculiarproperty of a magnet to transmit the vibrations of the diaphragm t0 theelectrodes to vary the resistance of the latter without requiring anydirect connection between the same. This I accomplish by placing apermanent or electro-inagnet behind, but preferably out of contact withthe diaphragm, and placing the electrode or electrodes preferably in theform of buttons in such position with relation to the -magnet, that thepressure upon or between the button or buttons will be varied by andwith the variations or changes in the form of the magnet due to thechanges in its magnetism. The vibrations of the metallic diaphragmtoward and from the end of the magnet cause the magnetism of the latterto be changed, and, therefore, its length or form to be also changed.These variations in length or form of the magnet are transmitted to andvary the resistance of the electrode or electrodes, said magnet, whenthe electrode or electrodes is or are in the form of a carbon or otherbutton or buttons acting upon and varying the pressure upon or betweenthe same. By such a construction the diaphragm is left entirely free tovibrate to its fullest extent under the influence of the sound wavesproduced by speaking; the contact between the electrode or electrodesmay be made as firm and rigid as found necessary for the best results,Without, in any degree, limiting the amplitude of the vibrations of thediaphragm; and the vibrations of the diaphragm at each side of itscentral or stationary position, both toward and from the end of themagnet, exert an influence upon the magnet and thereby upon theelectrodes. I am, therefore, enabled to obtain a much stronger andclearer transmission of speech than is possible in any transmitter nowknown to me.

Other features of this invention will be hereinafter described in thespecification and I pointed out in the claims.

Referring to the drawings, Figure l represents in vertical section oneform of transmitter embodying this invention; a single electrode beingshown resting directly against the magnet. Fig. 2 shows an irregularlyformed magnet. Fig. 3 shows my invention embodied in a construction,employing two electrodes which are pressed together, more or less, bythe change in form of the magnet. Fig.4:showsthemagnet actingupontheflexible side of a chamber containing pulverized carbon or resistantmaterial which constitutes the electrode or electrodes. Fig. 5 shows ahorseshoe magnet, in which lateral movement of the legs of the magnet iscaused by the changes in its magnetism, and Fig. 6 shows anelectro-magnet instead of a permanent magnet as in the otherconstructions.

In the form of transmitter selected by me to illustrate this invention(1 represents any usual or suitable diaphragm placed back of amouth-piece a, the same to receive the soundwaves set up byconversation, or speaking, directed toward it or in its vicinity. Backof this diaphragm, which will preferably be of metal, and which Idenominate hereinafter in the claims as the magnet influencing member,but preferably out of actual contact therewith at all times, is placed amagnet 17, preferably a permanent magnet, though an electro-magnet maybe used if desired, as will be hereinafter set forth, said magnet beingof any desired form or shape, it being shown in Fig. 1 as a straightbar-magnet.

In the embodiment of myinvention herein shown, I employ an electrode 0of carbon or other suitable or equivalent material, said electrode, asshown, being arranged adjacent to and preferably in direct contact withthe magnet, the said electrode, as herein shown,

resting against that end of the magnet oppo site the end facing thediaphragm, said electrode being supported in suitable manner, preferablyby a stifi arm 0', shown as turned at right angles at its upper end, andthreaded to receive the adjusting nut c acting between two ears 0rigidly supported within the box A of the transmitter, rotation of thenut in one or the-other direction varying the pressure with which theelectrode is pressed against the magnet.

In the transmitter shown, the magnet and electrode are included in theprimary circuit of an induction coil D, said circuit comprising a partof the transmitting circuit to convey the variations in resistance tothe distant receiver, said primary circuit, as herein shown, consistingof a wire 1 leading from one end of the coil to a binding screw'2,bywhich the magnet is also secured in its position in the inclosing case Aback of the diaphragm, the circuit passing thence through the magnet andelectrode, through the arm a of the latter, binding-post and wire 4 tothe opposite end of the primary coil of the induction coil and a battery0 included in said circuit. The secondary circuit 5 of theinductioncoil, the ends only of which are shown, completes the transmittingcircuit and leads tothe distant receiver, and need not be herein shownin diagram or detail as it is the same as in the usual transmitters nowin common use.

The operation of the transmitter is as follows, viz:Oonversationdirected toward the diaphragm causes the diaphragm to vibrate toward andfrom the end of the magnet I), though the diaphragm preferably nevercomes into direct contact with the end of the magnet, for reasonshereinbefore stated. These vibratory movements of the diaphragm,alternately toward and from the magnet in proximity thereto, act to varythe strength or polarity of the magnetism in the magnet, and, inaccordance with that peculiar property of magnets hereinbeforementioned, also vary its form or length at each change in its magnetismhowever slight that change may be. The variations in the length or formof the magnet act upon the electrode 0, held at one end in contacttherewith, to vary the pressure upon the same, and thereby interpose agreater or less resistance in the primary circuit of the induction coil.The variations in the resistance interposed in the primary circuit ofthe induction coil by the variations in pressure upon the electrode bythe magnet, correspond both in number and degree to the number andamplitude of the vibrations of the diaphragm under the influence of thesound- Waves, so that the undulations in the primary. .circuit of theinduction coil must correspond with or be the exact counterpart of thevibrations of the diaphragm and the undulations of the sound waves, theresult being that a corresponding undulatory current is induced or setup in the secondary circuit of'the coil,

which is received and made audible at and by the distant receiver inusual manner.

By reference to Fig. 1 it will be seen that the diaphragm, being freefrom contact at either side with any device whatever, is absolutely freeto vibrate under the influence of the sound waves, the amplitude of thevibrations beingldetermined solely by the sound waves and in no wiserestrained by any device rest ing upon or against it. It will also beseen that, inasmuch as the movements of a piece of metal away from amagnet exert an equal thorough opposite influence upon the magnet fromthe movements of the same piece of metal toward the magnet, thevibratory movements of the diaphragm receding from the magnet exert anequally strong influence upon the magnet with the vibrations of thediaphragm toward the magnet, so that the full amplitude of thevibrations of the diaphragm is utilized to transmit the effect of thesound waves to the distant receiver. In this respect my improvedtransmitter differs, as hereinbefore stated, from the transmitters nowin use, wherein the vibrations of the diaphragm are mechanicallytransmitted to the electrode, for, while in the mechanical transmissionof the vibrations to the electrode the vibratory movements of thediaphragm at one side the central position alone are utilized, in myimproved transmitter the vibratory movement of the diaphragm at eachside the central position, both toward and from the magnet, areutilized. Again, it has been found that the electrode or electrodes whenheld firmly or rigidly respond more accurately to the vibrations of thediaphragm than when supported by yielding springs, yet a rigidlysupported electrode if permitted to rest against the diaphragm, as inthe transmitter referred to now in use, would practically preventvibrations of the diaphragm. By referring to Fig. 1 however, it will beseen that in myimproved transmitter the electrode may, and

.preferably is firmly supported back of and in contact with the magnet,so that there can be no reactionary vibrations or movements of theelectrode independent of those set up by the changes in form of themagnet due to the vibrations of the diaphragm. The undulatory currenttraversing the transmitting circuitmust, therefore, correspond exactlywith the undulations in the sound waves produced by the speaking.

In Fig. 2, 1) represents an irregularly shaped magnet, in which theaction is substantially the same as in Fig. 1, this figure showing thatit is possible to carry the magnet to some point quite distant from thediaphragm, to thereby remove the delicate parts of the instrument fromthe vicinity of the diaphragm, when in such position they would belikely to receive injury.

Fig. 3 represents a construction corresponding somewhat to theconstruction of the well known Blake transmitter, in which twoelectrodes e, 6', independently supported upon stiff springs e e, arepositioned directly back of the magnet b, the pressure between theelectrodes being varied by changes in the form of the magnet due to thevibrations of the diaphragm.

Fig. at shows the magnet acting against the front wall f of a box orreceptacle f containing powdered charcoal or resistant material whichconstitutes the electrode or electrodes, as in the Hunning transmitter,the changes in form of the magnet pressing the flexible wall of thechamber-in or out with greater or less force to vary the pressure uponor between the particles of resistant material within the chamber.

In Fig. 5, b is a horse-shoe magnet, the dia-- phragm being moved towardand from one pole of the magnet, the changes in the magnetism caused bythe vibrations of the diaphragm manifesting themselves by a spreadingmovement of the legs of the magnet, so that the resistant electrode 0may in this instance rest against the side of the magnet instead ofagainst its end as in Fig. 1.

In Fig. 6 an electro-magnet is shown instead of a permanent magnet, theaction of the two being substantially the same.

This invention is not limited to any particular shape, arrangement, orconstruction of the various parts, as the same manifestly may be variedin many ways and still come within the scope of this invention.

I consider myself to be the first to change the form of a magnet bymoving an influencing member in proximity and with relation thereto, andutilizing the change in the form of the magnet thus produced to causevariations in the resistance in the electric transmitting circuit; andmy invention therefore, broadly speaking, consists in changing the formof a magnet and thereby the resistance in an electric transmittingcircuit by moving an influencing member in proximity to the magnet, theterm electric transmitting circuit as herein used and as hereinafteremployed in the claim, meaning any circuit which either directly, aswhen used for a line circuit, or indirectly, as for instance, whenconstitnting the primary circuit of an induction coil, the secondarycircuit of p which constitutes the line, assists in the transmission ofspeech to a distant receiver.

The invention also includes certain details of construction whereby I amenabled to carry out the principles of this invention.

I claim 1. In a telephone transmitter,a diaphragm, and a resistantelectrode adapted to be placed in an electric circuit, combined with amagnet arranged to be directly influenced by the vibrations of thediaphragm, and by its changes in form act upon and vary the resistanceinterposed by said electrode in said circuit, substantially asdescribed.

2. In a telephone transmitter, a diaphragm and an electrode adapted tobe placed in an electric circuit, combined with a magnet arranged to bedirectly influenced bythe vibrations of the diaphragm, and by itschanges in form act upon and vary the pressure uppn the said electrode,substantially as described.

3. In a telephone transmitter, a diaphragm 'and' an electrode adapted tobe included in an electric transmitting circuit, combined with a magnetrigidly held between the diaphragm and electrode, in contact with thelatter and in position close to the former so as to be influenced andchanged in form by the vibrations thereof, whereby the said changes inform of the magnet vary the pressure upon the electrode, substantiallyas described.

4:. In a telephone transmitter, a diaphragm and a fixed magnet arrangedback of and close to the same and to be influenced and changed in formby the vibrations of the diaphragm, combined with an electrode adaptedto be included in an electric transmitting circuit, and

